1. Field of the Invention
This invention relates to a semiconductor integrated circuit which can adjust its signal characteristics by itself when the characteristics fluctuate due to production variations, and to a method of the adjustment.
2. Description of the Related Art
When a semiconductor integrated circuit is produced with a semiconductor manufacturing process, it is common to have manufacturing variations in such as alignment of photomasks and width of an etched line. Characteristics of the semiconductor integrated circuit vary among semiconductor integrated circuits due to the manufacturing variations, even if they are from the same production lot or even from the same wafer.
For example, if the semiconductor integrated circuit includes an amplifier, the gain of the amplifier varies among the semiconductor integrated circuits. When the semiconductor integrated circuits are shipped to an electronic equipment manufacturer and mounted in electronic equipment, the characteristics of the equipment vary from unit to unit. With this being the situation, electronic equipment manufacturers used the semiconductor integrated circuits adjusting variations in the characteristics of the semiconductor integrated circuits themselves.
For example, a TV receiver manufacturer uses signal processing ICs which receive and demodulate video signals. The video signal processing ICs have various characteristics such as depth of color, tint, and brightness. Although these characteristics are modified to liking of the TV receiver manufacturer or of viewers, basic range of adjustment is determined by the manufacturer of the semiconductor integrated circuits. Each of the semiconductor integrated circuits needs to have the same basic range of adjustment. Otherwise, criteria of the adjustment to the electronic equipment would vary.
In reality, however, the characteristics vary among the semiconductor integrated circuits resulting from the variations in manufacturing of the semiconductor integrated circuits as described above. Thus, the TV receiver manufacturer have measured the variations in the characteristics of the semiconductor integrated circuits and adjusted them.
To explain more concretely, a TV receiver has a microcomputer and a memory. For example, depth of color is measured by an image scanner or by visual evaluation, and an adjustment signal is generated so that a center value of the color always has predetermined depth.
The adjustment signal value is calculated by the microcomputer and stored in the memory. Once stored in the memory, the adjustment signal is read from the memory by the microcomputer and applied to the video signal processing IC, every time the power supply of the TV receiver is turned on. By this means, always same amount of control can be applied to the TV receiver, whichever semiconductor integrated circuit is used as the video signal processing IC.
However, a problem is that the electronic equipment manufacturer, not the semiconductor integrated circuit manufacturer, has to make the adjustment of the variations in the semiconductor integrated circuits, bearing additional complication of adjustment processes in the production line.